1. Field of the Invention
The present invention relates to a developing apparatus for visualizing latent images, which is employed in an electronic photographing apparatus or a static recording apparatus, and more particularly to a developing apparatus capable of obtaining high-quality images with use of a one-component developing agent.
2. Description of the Related Art
As a developing method using a one-component developing, agent, there an impression development method is known. This method is characterized in that a static latent image is contacted with toner particles or a toner-carrying body at a substantially zero relative peripheral velocity (see U.S. Pat. Nos. 3,152,012; 3,731,146; Published Unexamined Japanese Patent Application (PUJPA) No. 47-13088; PUJPA No. 47-13089; etc.). Since no magnetic material is needed, there are many advantages; for example, simplification and miniaturization of the apparatus, and easy use of color toner.
In the above impression development method, development is performed in the state wherein the toner carrying body is pressed on, or put in contact with, a latent image. Thus, it is necessary to use a developing roller with elasticity and electrical conductivity. In particular, when the latent image carrying body is rigid, it is imperative that the developing roller be formed of an elastic material in order to prevent damage to the latent image carrying body. In order to obtain well-known developing electrode and bias effects, it is desirable to provide an electrically conductive layer on or near the surface of the developing roller, and apply a bias voltage as needed. However, where the conductive layer is provided on the surface of the elastic roller, the conductive layer pressure-contacts the latent image carrying body or a blade for forming a toner thin film. Consequently, damage, such as scars, may occur. Even if the bias conductivity is maintained by using an electrically conductive elastic body, photographic density non-uniformity, fog or scars may appear on the produced image.
In the above impression developing method, there is proposed a blade for forming a toner thin layer, an end portion of the blade having a curvature. Since this type of blade has a curved portion which contacts the developing roller, the thickness of the toner layer can be made uniform without increasing a linear load. On the other hand, however, unless the straightness of the curved portion of the blade in its longitudinal direction is increased, the density non-uniformity or irregular formation of the toner layer may occur in the longitudinal direction.